Due to its characteristics of being easily applicable to various products and electrical characteristics such as a high energy density, a secondary battery is not only commonly applied to a portable device, but universally applied to an electric vehicle (EV), a hybrid electric vehicle (HEV), or an energy storage system that runs on an electrical driving source. This secondary battery is gaining attention for its primary advantage of remarkably reducing the use of fossil fuels and not generating by-products from the use of energy, making it a new eco-friendly and energy efficient source of energy.
A secondary battery can be charged and discharged repeatedly by electrochemical reactions between elements including a positive electrode current collector, a negative electrode current collector, a separator, an active material, an electrolyte solution, and the like. By way of example, a lithium polymer secondary battery being widely used has an operating voltage in the range of about 3.7V to about 4.2V. Accordingly, to obtain a high power battery pack for use in an electric vehicle, a plurality of unit secondary battery cells are connected in series to construct a battery pack.
In addition to this basic structure, the battery pack further includes a battery management system to monitor and control a state of a secondary battery by applying an algorithm for control of power supply to a driving load such as a motor, measurement of electrical characteristic values such as current or voltage, charge/discharge control, voltage equalization control, state of charge (SOC) estimation, and the like.
Recently, with the increasing need for a high-capacity structure as well as utilization as an energy storage source, the demand for a battery pack of a multi-module structure in which a plurality of battery modules including a plurality of secondary battery cells are assembled, is also increasing.
Because the battery pack of the multi-module structure includes a plurality of secondary battery cells, there is a limitation in controlling the charge/discharge state of all the secondary battery cells or the plurality of battery modules using a single battery management system. Accordingly, a recent technology has been introduced in which a battery management unit is mounted in each battery module included in the battery pack, the battery management units are designated as a slave unit, a master unit is additionally provided to control the slave units or at least one of the slave units is designated as a master unit, and the master unit and the slave units make up a battery management system.
In this instance, the battery management units included in the battery management system output, to an external device, a signal indicating whether an error occurred in the secondary battery cells the battery management units manage. However, when a circuit or wiring used to transmit the notification of whether an error occurred is faulty, a signal indicating whether an error occurred is not transmitted despite an error or malfunction occurred in the battery management unit, and in contrast, the battery management unit is in normal state, but nevertheless, a signal indicating that an error occurred in the battery management unit may be transmitted. Accordingly, it is difficult to identify whether an error occurred in the battery management unit itself, or a circuit, a switching device, or a signal line inside the battery management system.